Marquez and Pacquiao fought to a 2004 draw, then battled to a split-decision won by Pacquiao in 2008. Part three of the trilogy appears destined for MGM Grand Garden Arena in Las Vegas, with Pacquiao's World Boxing Organization welterweight belt on the line.

Kimmel and Pacquiao even performed a duet -- back to back (perhaps to avoid eye contact?) of "How Deep Is Your Love" with a good deal of falsetto.

Pacquiao may be exercising his vocal cords with Kimmel, but he's also been seriously exercising his fists in preparation for the bout. At his Hollywood gym, he has taken on pro boxers, who are offered $1,000 if they can knock him down. So far, no one has done it.

As for any superfight between Pacquiao and Floyd Mayweather Jr.? Pacquiao says he's indifferent: "I don't need him in my boxing career. I'm already satisfied with what I've achieved in boxing. I think I accomplished all of my dreams."